The ExtKeyDictionary class encapsulates the behavior required to access entries in external key dictionary subclasses.
External key dictionaries are dictionaries in which the keys are not derived from the properties in the member objects but are external values supplied as parameters to the access methods.
The add, remove, and includes methods are defined at the Collection class level to provide closure and are inherited by all subclasses of collection. However, use of these Collection class methods with external key dictionaries is not recommended because none of the method signatures allow for the specification of external keys.
For details about accessing dictionary keys and the methods defined in the ExtKeyDictionary class, see "Using Subscripts in Dictionaries" and "ExtKeyDictionary Methods", in the following subsections.